Google Inc.’s YouTube may give viewers the option to watch ad-free videos for a fee, according to a top executive at the Internet giant, a big change from the advertising-only approach that turned it into the world’s largest online video website.

The change is being led by Susan Wojcicki, a veteran Google executive who spent years on the advertising side of the company. She took over YouTube earlier this year and has been looking for ways to generate more revenue and profit from the video site, which Google acquired for $1.65...